Problem: $ { {-5} \times \left[\begin{array}{rr}{4} & {2} \\ {-2} & {1} \\ {3} & {1}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-5}\times{4} & {-5}\times{2} \\ {-5}\times{-2} & {-5}\times{1} \\ {-5}\times{3} & {-5}\times{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-20} & {-10} \\ {10} & {-5} \\ {-15} & {-5}\end{array}\right]}$